//计算响应头的中间件
module.exports = async(ctx, next) => {
    const contentType = 'application/json; charset=utf-8'
    ctx.set('Content-Tyoe', contentType)
        //设置允许跨域请求
    ctx.set("Access-Control-Allow-Origin", "*")
    ctx.set("Access-Control-Allow-Methods", "OPTIONS,GET,PUT,POST,DELETE")
    await next()
}